A heat insulation part embodied as a slotted disc is known, which is pressed by a tightening nut against the shoulder of the recessed bore of the cylinder head of the internal combustion engine. A sleeve-like heat insulation part is also known, whose outer collar is likewise pressed by the tightening nut against the shoulder of the recessed bore of the cylinder head.
The heat insulation part is of course replaced by a new part whenever the nozzle is changed. When the tightening nut is pushed out of the cylinder head, the nozzle is simultaneously expelled along with it; however, the heat insulation part is not. Particularly after a relatively long time in operation, the heat insulation part is usually stuck in place in the cylinder head, so that loosening and removing this part necessitates additional expense.